In connection with surgery for a number of diseases in the gastro-intestinal tract, one of the consequences in many cases is that the patient is left with an abdominal stoma, such as a colostomy or an ileostomy in the abdominal wall for the discharge of visceral contents. The discharge of visceral contents, including intestinal gases, cannot be regulated at will. For that purpose, the user will have to rely on an appliance to collect the material emerging from such opening in a bag, which is later emptied and/or discarded at a suitable time.
The discharge of flatus, measured in volume, may exceed the discharge of solid and liquid faecal matter by many hundreds of percent, and therefore there is usually the need for the continuous or frequent venting of the intestine or the collecting bag. Normally the out-flowing flatus is deodorised with a suitable filter. Commonly, the active filter is powdered active carbon, which absorbs H2S being the principal component of the smell of flatus.
During use of a collecting bag, the output from a colostomy or an ileostomy may stick on the face of the filter facing inwards in the collecting bag. This will eventually lead to clogging of the filter, thereby reducing the flow through the filter. When the filter is completely blocked, it will stop functioning and the bag will fill with gases and expand, an effect also known as ballooning. This may cause embarrassment to the user, as the bag will be noticeable through the clothing. It may also cause detachment of the appliance from the user's skin—or detachment of the pouch from the wafer.